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Coding Standards

shFlags is more than just a simple 20 line shell script. It is a pretty significant library of shell code that at first glance is not that easy to understand. To improve code readability and usability, some guidelines have been set down to make the code more understandable for anyone who wants to read or modify it.

Function declaration

Declare functions using the following form:

doSomething() {
  echo 'done!'
}

One-line functions are allowed if they can fit within the 80 char line limit.

doSomething() { echo 'done!'; }

Function documentation

Each function should be preceded by a header that provides the following:

  1. A one-sentence summary of what the function does.

  2. (optional) A longer description of what the function does, and perhaps some special information that helps convey its usage better.

  3. Args: a one-line summary of each argument of the form:

    name: type: description

  4. Output: a one-line summary of the output provided. Only output to STDOUT must be documented, unless the output to STDERR is of significance (i.e. not just an error message). The output should be of the form:

    type: description

  5. Returns: a one-line summary of the value returned. Returns in shell are always integers, but if the output is a true/false for success (i.e. a boolean), it should be noted. The output should be of the form:

    type: description

Here is a sample header:

# Return valid getopt options using currently defined list of long options.
#
# This function builds a proper getopt option string for short (and long)
# options, using the current list of long options for reference.
#
# Args:
#   _flags_optStr: integer: option string type (__FLAGS_OPTSTR_*)
# Output:
#   string: generated option string for getopt
# Returns:
#   boolean: success of operation (always returns True)

Variable and function names

All shFlags specific constants, variables, and functions will be prefixed appropriately with 'flags'. This is to distinguish usage in the shFlags code from users own scripts so that the shell name space remains predictable to users. The exceptions here are the standard assertEquals, etc. functions.

All non built-in constants and variables will be surrounded with squiggle brackets, e.g. ${flags_someVariable} to improve code readability.

Due to some shells not supporting local variables in functions, care in the naming and use of variables, both public and private, is very important. Accidental overriding of the variables can occur easily if care is not taken as all variables are technically global variables in some shells.

Type Sample
global public constant FLAGS_TRUE
global private constant __FLAGS_SHELL_FLAGS
global public variable flags_variable
global private variable __flags_variable
global macro _FLAGS_SOME_MACRO_
public function flags_function
public function, local variable ``flags_variable_`
private function _flags_function
private function, local variable _flags_variable_

Where it makes sense to improve readability, variables can have the first letter of the second and later words capitalized. For example, the local variable name for the help string length is flags_helpStrLen_.

There are three special-case global public variables used. They are used due to overcome the limitations of shell scoping or to prevent forking. The three variables are:

  • flags_error
  • flags_output
  • flags_return

Local variable cleanup

As many shells do not support local variables, no support for cleanup of variables is present either. As such, all variables local to a function must be cleared up with the unset built-in command at the end of each function.

Indentation

Code block indentation is two (2) spaces, and tabs may not be used.

if [ -z 'some string' ]; then
  someFunction
fi

Lines of code should be no longer than 80 characters unless absolutely necessary. When lines are wrapped using the backslash character '', subsequent lines should be indented with four (4) spaces so as to differentiate from the standard spacing of two characters, and tabs may not be used.

for x in some set of very long set of arguments that make for a very long \
    that extends much too long for one line
do
  echo ${x}
done

When a conditional expression is written using the built-in [ command, and that line must be wrapped, place the control || or && operators on the same line as the expression where possible, with the list to be executed on its own line.

[ -n 'some really long expression' -a -n 'some other long expr' ] && \
    echo 'that was actually true!'